Translations on this website are prepared by a third-party provider. Some portions may be incorrect. Some items—including downloadable files or images—cannot be translated at all. No liability is assumed by Beth Israel Deaconess Medical Center for any errors or omissions. Any user who relies on translated content does so at his/her own risk.

New Insight Into Course and Transmission of Zika Infection

Evidence suggests virus may be sexually, orally transmitted

BOSTON – Though first documented 70 years ago, the Zika virus was poorly
understood when it burst onto the scene in the Americas in 2015. In one of
the first and largest studies of its kind, a research team lead by
virologists at Beth Israel Deaconess Medical Center (BIDMC) has
characterized the progression of two strains of the viral infection. The
study, published online this week in Nature Medicine, revealed Zika’s rapid infection of the brain and nervous tissues, and
provided evidence of risk for person-to-person transmission.

“We found, initially, that the virus replicated very rapidly and was
cleared from the blood in most animals within ten days,” said corresponding
author James B. Whitney, PhD, a principal investigator at the Center for Virology and Vaccine Research (CVVR) at BIDMC. “Nevertheless, we observed viral shedding in other bodily
fluids such as spinal fluid, saliva, urine and semen, up to three weeks
after the initial infection was already cleared.”

Whitney and colleagues infected 36 rhesus and cynomolgus macaques with
strains of the Zika virus derived from Puerto Rico and Thailand. Over the
next four weeks, the scientists tested blood, tissues, cerebrospinal fluid
(CSF) and mucosal secretions for the presence of Zika virus, as well as
monitored the immune response during early infection. Their data shed new
light on the previously little-studied virus, and might help explain how
Zika causes the devastating neurological complications seen in adults and
unborn babies.

“Of particular concern, we saw extraordinarily high levels of Zika virus in
the brain of some of the animals – the cerebellum, specifically – soon
after infection,” said Whitney, who is also assistant professor of medicine
at Harvard Medical School and an associate member of the Ragon Institute of
MGH, MIT, and Harvard. “Only one in five adults has noticeable symptoms of
infection. However, if our data translate to humans, there may be need for
enhanced clinical vigilance for any persons presenting with unusual
neurological symptoms, and they should be tested for Zika infection.”

Like in humans, Zika infection in the experimental primates appeared
relatively mild, producing fever and an increase in blood cells associated
with the immune response. All recovered without intervention. But while the
virus was cleared from the blood stream within ten days, the researchers
observed Zika virus in urine as soon as two days after infection in some
subjects. By the third day after infection, Zika was detectable in the
saliva of up to half of the subjects, where it remained until the study
ended at 28 days after infection.

“This underscores the need to understand what’s happening in anatomic
reservoirs where the virus may hide for a long time,” said Whitney.

Early in infection, the researchers found high levels of Zika in the
genital tracts of both sexes. Zika remained detectable in semen and in
uterine tissues until the end of the study. The first sexually transmitted
case of Zika in humans was documented in 2007, but these new findings
suggest transmission may occur long after Zika symptoms – if they ever
appeared – resolve. Because the researchers found high levels of the virus
in semen and uterus, but little in vaginal secretions, the findings may
also illuminate sexual transmission of Zika.

“We found that male-to-female transmission may be easier, while
female-to-male may be less likely,” said Whitney. “Nonetheless, the high
levels of Zika we observed in the uterus underscore the danger to a
developing fetus.”

The new study also highlights the need for the rapid development of vaccines and therapies against the virus. Zika infection in pregnant women has been
shown to lead to fetal microcephaly and other major birth defects. The World Health Organization declared the virus epidemic a global public health emergency on February 1,
2016.

About Beth Israel Deaconess Medical Center

Beth Israel Deaconess Medical Center is a patient care, teaching and research affiliate of Harvard Medical School and consistently ranks as a national leader among independent hospitals in National Institutes of Health funding.

BIDMC is in the community with Beth Israel Deaconess Hospital-Milton, Beth Israel Deaconess Hospital-Needham, Beth Israel Deaconess Hospital-Plymouth, Anna Jaques Hospital, Cambridge Health Alliance, Lawrence General Hospital, MetroWest Medical Center, Signature Healthcare, Beth Israel Deaconess HealthCare, Community Care Alliance and Atrius Health. BIDMC is also clinically affiliated with the Joslin Diabetes Center and Hebrew Rehabilitation Center and is a research partner of Dana-Farber/Harvard Cancer Center and the Jackson Laboratory. BIDMC is the official hospital of the Boston Red Sox. For more information, visit www.bidmc.org